Process of treating carbonaceous articles



Patented 5, 1931 UNITED STATES MICHAEL J. mom, 0]! TBENTON, IN'IEIT JERSEY, ASSIGNOR OI ONE-HALF MACKENZIE, TRENTON, NEW JERSEY PATEN OFFICE 1'0 DUNCAN PROCESS OF TREATING CARBONACEOUS ARTICLES No Drawing.

This invention relates to carbonaceous articleshavin a hard non-oxidizing surface and to a met 0d of treating carbonaceous-M1,

and dense, ,possesses substantially the same low coflicient of expansion as graphite, and forms substantially an integral part of the article and increases the resistance of the article to'fracture' Another object of the invention is to provide an economical and practical method-of treating carbonaceous articlesof all shapes as above described and which method allows control of-thedepth of the coating.

Heretofore, articles of this character have not been produced with a hard, -dense, nonoxidizing surface, nor was any method known whereby the depth of the treatment could be contrhlled with an accuracy. v

- According to t e present invention, carbonaceous articles are acked in a mixturiof finelydividedflint an carbon and the temperature raised sufliciently high to "produce a surface on the articles treated consisting substantially of silicon carbide. By 'flint is rials such as sand cant the purer forms of silica used in the g as and ceramic industries, but I donotre strict myself thereto, as other silicious m'ategiive equivalent results when used as herein sclosed; .By carbonaceous materials is meant graphite, coke, gas

' carbon, lamp black, and mixtures redomina'ntly of carbon with iilay etc, suc as used in crucibles and other refractories. -Carbo.

naceous materials as herein used, are also free of h drocarbons or other volatiles;

T is treatment may be carried out by embedding the articles in a mixture of flint and 'filielydivided carbon or coke and then heating the-mass'to a temperature suflicient to effeet the combination with the carbon of the of or more.

Application filed August 29, 1930. Serial No. 478,759.

-articles,'temperatures between about '3180 F.

to 60009 F. being suitable for this. The depth of the coating is dependent upon the temperature and length of time of treatment.

The treatment is carried out in an induction furnace of commercial, intermediate, or high frequency,- as articles of all shapes can be more uniformly heated and the treatment better controlled. The articles to betreated are placed in a container together with a mixture of flint and finely divided coke, the proportion of'fiint to coke preferably being about '63 parts by weight to 26 parts by weight, and

the container, usually a tube or crucible is fitted into the coil of an induction furnace and the current turned-on.

By usingan induction furnace the articles tobe treated are uniformly heated and the temperature and period of heating can be accurate-1y controlled to give the desired depth of coating. The size and shape of thearti cle to be coated presents no difliculty as the heating is uniform throughout as contrasted with the irregular heating effected by a furuace heated'from outside or one having a central core resistor through which the current is passed. Furthermore, in treating :carbonaceous articles as described in an induction furnace, a uniform homogeneous dense la er of *suflficient depth toadequately protect t e article canbe attained with case. In the case of large articles this layer may extend to a depth Auniform layer .of such depth 'has not heretofore been commercially possible, and such articles as I have produced have not been commercially known.

carbonaceous articles treated b my process have an" integral dense 'sur ace which seems tobe very pure silicon carbon, is homogeneous throughout, has substantially the same lowcoeflicient of expansion as the material of the article has a hardness of upwards of 7 on th ohs scale, in most instances a hardness of 9 on the. Mohs scale, is

non-oxidizin even at very high tem ra.- turos, and is 511 emically resistant to aci alkalies, etc.- The layer is also free of fluxes or slags.

The pro rtion of flint to coke in the mixture in which the articles are embedded may having be varied but to produce a uniform, homogeneous and hard surface la er, a mixture of about 63 parts by weight 0 .flint to 26 parts by weight of coke is most suitable.

The process is applicable-to articles of carbon, graphite, graphite-clay mixtures and the like.

The following example is given to specifically illustrate the invention.

A crucible inade of Acheson graphite and measuring 4" outside diameter, 3 inside diameter andi8" in length, wascoated as follows: A quartz cylinder with a closedbottom, 10 inside diameter and 15" long, was packed with the crucible embedded in a mixture of flint and coke of the following composition, 445 ounces of comminutedint and finely divided coke, the mixture being in the proportion of 63 parts by. weight of flint to 26 parts by weight of coke. The flint, such as used for fine porcelain' h'a'd the followinganalysis:

. Per cent Silica 99.43 Alumina 0.19 Titanium 3 0.03 Calcium 0.11 Magnesia 0.02 Iron .trace Ajax-Northrup 60,000 cycle converter, the

current turned on' and the converter adjusted to supply 11 k. w. to the induction coil holding t e cylinder. This was/permitted to run .2 hours at a total consumption of 22 k. w. h.

The temperature by pyrometer was above 3500- F, The current was then turned off and the mass'permitted to cooland the crucible removed.

The crucible was uniformly coated throughout with a uniform, homogeneous, andhard coating of silicon carbide. The coating showed a hardness of 9 on the Mohs scale and was about 1/ 'deep..

It has been found advantageous to add a small amount, approximately 1 part, of high grade beach sand to the mixture of flint and carbon. By the use'of this small proportion of sand, a,:coating is produced-which is more resistant to cracking that might. be caused through rough handling of the coated article.

This advantage is less pronounced in a rigid garticle, such as a crucible'where there is little likelihood of cracks developing under usual conditions.

Carbonaceous articles containing up to 40% of'inert material such as clay have been ceramic testing furnaces, kilns, etc., without .geneous and hard silicon carbide.

con carbide.

successfully coated by the process-herein described.

Electric furnace resistors made according to this process have been used substantially as produced from the furnace in heat treating, 7o

requiringpacking or other protective covering. Also, by this process the complete length of the resistor up to the metallic terminals can be protected so that special'fittin are not necessary where connections are ma e with terminals, bus bars-and the like. Further, resistors made according to this process only have their ohmic resistance increased up to about 20% when cold; whenheated' the conductivity is the same as graphite or carbon but the saving effected by elimination of packing, etc., with my electrodes is much greater ,than the cost of slightly more cross section 'to obtain the desired conductivity. Also, by reason of'eliminating packin a hot resistor of this invention can be pulled ou't of the furnace and another put in without cooling the furnace which so far as I am aware has not heretofore been possible.

The invention claimed is a 1. Process of treating-carbonaceous, arti= cles comprising embedding the same in' a mixture of flint and carbon, placing the mass in an induction furnace, and passing a current through said furnace to raise the temperature sufiiclently above the va rization point of flint and below the vaporization point of carbon to form an adherent surface layer of uniform. homogeneous and hard silicon-carbide.

2. Process for treating hollow carbona: ceous articles comprising embedding the same in a mixture of flint and carbon, placing the mass inan induction furnace centrally of the flux, and passing a current through said furnace to raise the temperature sufliciently above the vaporization oint of flint and below the vaporization point of carbon to form an adherent surface layer of uniform, homo- 3. Process of treating carbonaceous articles comprising embedding same in'a mixture of 63 parts by weight of flint to 26partsby weight finely divided coke, placing the mass in an induction furnace, and passing a 1 current through said furnaceto raise the temperature sufliciently above the vaporization po nt of flint and below the vaporization point of carbon to form an adherent surface layer of uniform, homogeneous and hard sin-1 Signed at New York, in the county of New York and State of New York this 28th day of August A. D. 1930.

MICHAEL J. MARCIN. 

